CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) shares in Millions, $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Accounts and notes receivable, allowance for doubtful accounts	$ 90	$ 72
Preferred stock, par value (in usd per share)	$ 0.01	$ 0.01
Preferred stock, authorized (in shares)	25	25
Preferred stock, outstanding (in shares)	0	0
Common stock, par value (in usd per share)	$ 0.01	$ 0.01
Common stock, authorized (in shares)	6,000	6,000
Common stock, issued (in shares)	1,943	1,985
Common stock, outstanding (in shares)	1,943	1,985